Despite the importance of airway smooth muscle excitability in reactive airway disease, very little information is currently available with respect to the precise ionic mechanisms which mediate the neurotransmitter induced excitation of this tissue. Further, the cellular mechansim or mechanisms by which important mediators of bronchoconstriction such as leukotrienes and histamine trigger contraction in airway smooth muscle is not know. This proposal seeks to apply recently developed advances in cell disaggregation and gigaseal recording techniques to isolate specific ion currents in single mammalian airway smooth muscle cells. Ion currents will be identified and studied in isolated airway myocytes from the ferret trachealis muscle by dialyzing the cells with impermeant ions, and using specific channel blocking agents. Specific ion currents will be studied under voltage clamp conditions to determine time-dependent and voltage dependent channel activation and inactivation characteristics. Experiments will be performed to determine if neurotransmitters and bronchoactive agents act by gating these currents. The working hypothesis of this proposal is that cell membrane receptor binding of neurohormonal agents gates an inward calcium current which initiates cell activation. This hypothesis will be examined by resolving whole cell calcium currents at fixed voltage in the presence of varying concentrations of these agents. These studies will thus provide important information about the membrane ionic processes regulating contraction, and the extent to which these processes are important in the response of airway smooth muscle to bronchoconstrictive agents which have been shown to be important mediators of airway hyperreactivity.